Post deposition adjustment of chalcogenide composition in chalcogenide containing semiconductors

ABSTRACT

The concentration of a constituent within a chalcogenide film used to form a chalcogenide containing semiconductor may be adjusted post deposition by reacting the chalcogenide film with a material in contact with the chalcogenide film. For example, a chalcogenide film containing tellurium may be coated with a titanium layer. Upon the application of heat, the titanium may react with the tellurium to a controlled extent to reduce the concentration of tellurium in the chalcogenide film.

BACKGROUND

This relates generally to chalcogenide containing semiconductors,including phase change memories and ovonic threshold switches.

Chalcogenide containing semiconductors include a chalcogenide layerwhich is an alloy of various chalcogens. For example, the well known GSTalloy is a composite of germanium, antimony, and tellurium. Many otheralloys are known. In addition to alloys used in phase change memories,chalcogenide alloys are also used for ovonic threshold switches, thedifference being that the chalcogenide layer in the ovonic thresholdswitch normally does not change phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, cross-sectional view at an early stage ofmanufacture according to one embodiment; and

FIG. 2 is an enlarged, cross-sectional view at a subsequent stage inaccordance with one embodiment.

DETAILED DESCRIPTION

In some cases, it is advantageous to adjust the composition ofchalcogenide layers deposited to form chalcogenide containingsemiconductor devices, including phase change memories and ovonicthreshold switches. For example, in some cases, it may be appreciatedthat finer control may be achieved post deposition than is possiblethrough the adjustment of the deposition process. Thus, in someembodiments, after the material is actually deposited, its chemicalcomposition can be altered.

In accordance with one embodiment, the chemical composition may bealtered by subsequently depositing a metal film that is reactive withone or more constituents of the deposited chalcogenide film. Upon heatactivation, a reaction occurs which depletes the targeted component fromthe chalcogenide film through reaction with the contacting metal film.The extent of the depletion may be controlled by the amount of thethermal budget and the thickness of the contacting metal film.

Thus, as one example, a GST chalcogenide may be coated with a layer oftitanium. When exposed to heat, the titanium reacts with the telluriumin the GST film and, as a result, depletes the tellurium. In this way,the tellurium composition can be adjusted post deposition.

As another example, titanium may be coated on IST (Indium AntimonyTellurium) phase change material. Also, titanium may be deposited on anovonic threshold switch material including tellurium.

In many cases, the extent of alteration can be controlled with aconsiderable degree of precision because it is a function of time,temperature, and deposited material thickness.

In some cases, the subsequent post deposition adjustment may bepreplanned and may be part of the overall recipe for forming thesemiconductor device. In other cases, testing of the chalcogenide filmsas deposited may suggest a need for fine adjustment, rather thanproducing less than ideal devices or destroying the wafers with thedeposited chalcogenide film.

Thus, for example, referring to FIG. 1, an example of a chalcogenidecontaining semiconductor 10 may include a bottom electrode 12, achalcogenide film 14, a thin titanium film 16 deposited thereover, and atop electrode 18.

The structure 10, shown in FIG. 1, may then be subjected to sufficientheating to create a reaction between tellurium in the chalcogenide film14 and the titanium film 16. As a result, the tellurium reacts with thetitanium film to form the titanium tellurium based alloy film 16 a,shown in FIG. 2. Due to heating, the tellurium diffuses into thetitanium film 16 and reacts with the film 16. The chalcogenide film 14 ahas now been depleted of tellurium to a controlled extent in someembodiments. The extent of depletion is controlled based on thermalbudget and titanium layer thickness.

The same concepts can be applied to any chalcogenide alloy or phasechange material formed by physical vapor deposition or chemical vapordeposition, as two examples. Thus, for example, the film 14, in oneembodiment, may be GST and the electrodes 12 and 18 may be titaniumnitride.

Also, selenium in chalcogenide material may be reacted a titanium metalcoating. Cobalt metal may also react with tellurium in the chalcogenide.

Programming to alter the state or phase of the material may beaccomplished by applying voltage potentials to address lines, therebygenerating a voltage potential across a memory element including a phasechange film 14 a. When the voltage potential is greater than thethreshold voltages of any select device and memory element, then anelectrical current may flow through the phase change film 14 a inresponse to the applied voltage potentials, and may result in heating ofthe phase change film 14 a.

This heating may alter the memory state or phase of the film 14 a, inone embodiment. Altering the phase or state of the film 14 a may alterthe electrical characteristic of memory material, e.g., the resistanceor threshold voltage of the material may be altered by altering thephase of the memory material. Memory material may also be referred to asa programmable resistance material.

In the “reset” state, memory material may be in an amorphous orsemi-amorphous state and in the “set” state, memory material may be in acrystalline or semi-crystalline state. The resistance of memory materialin the amorphous or semi-amorphous state may be greater than theresistance of memory material in the crystalline or semi-crystallinestate. It is to be appreciated that the association of reset and setwith amorphous and crystalline states, respectively, is a convention andthat at least an opposite convention may be adopted.

Using electrical current, memory material may be heated to a relativelyhigher temperature to melt and then quenched to vitrify and “reset”memory material in an amorphous state (e.g., program memory material toa logic “0” value). Heating the volume of memory material to arelatively lower crystallization temperature may crystallize ordevitrify memory material and “set” memory material (e.g., programmemory material to a logic “1” value). Various resistances of memorymaterial may be achieved to store information by varying the amount ofcurrent flow and duration through the volume of memory material.

An ovonic threshold switch is either on or off depending on the amountof voltage potential applied across the switch and, more particularly,whether the current through the switch exceeds its threshold current orvoltage, which then triggers the device into an on state. The off statemay be substantially electrically non-conductive and the on state may bea substantially conductive state with less resistance than the offstate.

In the on state, the voltage across the switch, in one embodiment, isequal to its holding voltage V_(hold)+IR_(on), where R_(on) is thedynamic resistance from the extrapolated X axis intercept V_(hold). Forexample, an ovonic threshold switch may have a threshold voltage V_(th)and, if a voltage potential less than the threshold voltage of theswitch is applied across the switch, then the switch may remain off orin a relatively high resistance state so that little or no electricalcurrent passes.

Alternatively, if a voltage potential greater than the threshold voltageof the select device is applied across the device, then the device mayturn on, i.e., operate in a relatively low resistance state so thatsignificant electrical current passes through the switch. In otherwords, one or more series connected switches may be in a substantiallyelectrically non-conductive state at less than a predetermined voltage,e.g., the threshold voltage as applied across a switch. The switch maybe in a substantially conductive state if greater than a predeterminedvoltage is applied across the switch.

In one embodiment, each switch may comprise a switch material that is achalcogenide alloy. The switch material may be a material in asubstantial amorphous state positioned between two electrodes that maybe repeatedly and reversibly switched between a higher resistance offstate that is generally greater than about 1 megaOhms and a relativelylower resistance on state that is generally less than about 1000 Ohms inseries with the holding voltage by the application of electrical currentor potential.

Each switch is a two-terminal device that has an IV curve similar tothat of a phase change memory element that is in an amorphous state.However, unlike a phase change memory element, the ovonic thresholdswitch does not change phase. That is, the switching material of theovonic threshold switch is not a phase programmable material and, as aresult, the switch may not be a memory device capable of storinginformation. For example, the switching material may remain permanentlyamorphous and the IV characteristics may remain the same throughout theoperating life.

In the low voltage, low electric field mode, where the voltage appliedacross the switch is less than the threshold voltage V_(th), the switchmay be off or non-conducting and exhibits a relatively high resistance.The switch may remain in the off state until a sufficient voltage,namely, the threshold voltage, is applied or a sufficient current isapplied, namely, the threshold current, that switches the device to aconductive relatively low resistance on state. After a voltage potentialof greater than about the threshold voltage is applied across thedevice, the voltage potential across the device may drop or snapback toa holding voltage V_(hold). Snapback may refer to the voltage differencebetween the threshold voltage and the holding voltage of the switch.

In the on state, the voltage potential across the switch may remainclose to the holding voltage as current passing through the switch isincreased. The switch may remain on until the current through the switchdrops below a holding current. Below this value, the switch may turn offand return to a relatively high resistance, non-conductive off state,until the threshold voltage and current are again exceeded.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such forms may be encompassed within the claims of the presentapplication.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A method, comprising: depositing a chalcogenidefilm on a first electrode, wherein a portion of the chalcogenide filmcontacts the first electrode, wherein the first electrode includestitanium nitride; depositing a titanium film over the chalcogenide film;depositing a second electrode on the titanium film, wherein the secondelectrode includes titanium nitride; and altering, the composition ofthe chalcogenide film.
 2. The method of claim 1, wherein altering thecomposition of the chalcogenide film comprises reducing theconcentration of one component of the chalcogenide film.
 3. the methodof claim 1, wherein altering the composition of the chalcogenide filmcomprises applying heat to react a constituent of the chalcogenide filmwith the titanium film.
 4. The method of claim 1, wherein altering thecomposition of the chalcogenide film further comprises diffusing acomponent or the chalcogenide film into the titanium film.
 5. The methodof claim 1, wherein the chalcogenide film includes tellurium, andwherein the titanium film is reactive with the tellurium.
 6. The methodof claim 1, wherein depositing the chalcogenide film on the electrodecomprises depositing the ehalcogenide film on a surface of theelectrode.
 7. A method comprising: depositing a chalcogenide film on afirst electrode, wherein a portion of the chalcogenide film contacts thefirst electrode, wherein the first electrode includes titanium nitride;depositing a metallic film on the chalcogenide film, wherein themetallic film includes titanium; depositing a second electrode on themetallic film, wherein the second electrode includes titanium nitride;and heating the chalcogenide film and the metallic film to reduce theconcentration of material of the chalcogenide film.
 8. The method ofclaim 7, wherein the chalcogenide film comprises a germanium, antimony,and tellurium (GST) alloy.
 9. The method of claim 8, further comprisingreacting the metallic film with at least the tellurium of the GST alloy.10. A method, comprising; forming a chalcogenide film on a firstelectrode, wherein a portion of the chalcogenide film contacts the firstelectrode, wherein the first electrode includes titanium nitride;depositing another material on the chalcogenide film, wherein theanother material includes titanium; depositing a second electrode on themetallic film, wherein the second electrode includes titanium nitride;and treating the chalcogenide film to reduce the concentration of amaterial of the chalcogenide film.
 11. The method of claim 10, whereintreating the chalcogenide film to reduce the concentration of thematerial of the chalcogenide film comprises applying heat to react theanother material with the material of the chalcogenide film.
 12. Themethod of claim 11, wherein the material includes tellurium.
 13. Amethod, comprising: forming a first electrode; depositing a chalcogenidefilm on the first electrode, wherein a portion of the chalcogenide filmcontacts the first electrode; forming a metallic layer on thechalcogenide film, wherein the metallic layer includes titanium; forminga second electrode on the metallic film, wherein the second electrodeincludes titanium nitride; and altering a composition of thechalcogenide film by reacting the chalcogenide film with the metalliclayer.
 14. The method of claim 13, wherein changing a composition of thechalcogenide film by reacting the chalcogenide film with the metalliclayer comprises heating the chalcogenide film and the metallic layer.15. The method of claim 14, wherein changing a composition of thechalcogenide film by reacting the chalcogenide film with the metalliclayer comprises transferring a portion of a material of the chalcogenidefilm to the metallic layer responsive to the heating of the chalcogenidefilm and the metallic layer.